In-borehole gas monitor apparatus and method comprising a voc concentration analyser and a voc collector

ABSTRACT

In-Borehole Gas Monitor Apparatus and Method An in-borehole gas monitor (IGM) apparatus comprising a VOC concentration analyser and a VOC collector.

FIELD OF THE INVENTION

The present invention relates to in-borehole gas monitor (IGM) apparatusand methods.

BACKGROUND TO THE INVENTION

The monitoring of gas concentrations, and in particular methane andcarbon dioxide, generated by landfill and associated sites is becoming amore common legislative requirement due to the potential problems thesegases pose, such as the risk of explosion and impacts as greenhousegases. At present, the majority of landfill gas analysis is achievedeither through spot sampling or through the use of large expensive fixedposition monitoring stations. More recently it has been recognised thatgas production and migration responds to environmental factors such asbarometric pressure and groundwater movement, with the accompanyingrealisation that spot sampling will often miss such changes.

It is known from WO 2007/141512 to provide a self-contained IGMapparatus comprising a detector for measuring a gas variable, and acontroller configured to automatically periodically use the detector tomeasure a gas variable.

However, the apparatus and method disclosed in WO 2007/141512 do notdeal with volatile organic compounds (VOCs).

It is an aim of preferred embodiments of the present invention toaddress, overcome or obviate a disadvantage of the prior art, whethersuch prior art or disadvantage is referred to herein or otherwise.

SUMMARY OF THE INVENTION

According to the present invention in a first aspect, there is providedan in-borehole gas monitor (IGM) apparatus comprising a VOCconcentration analyser and a VOC collector.

Suitably, the VOC concentration analyser is configured to provide anon-specific real-time concentration of VOCs. Suitably, the VOCconcentration analyser comprises a photo-ionisation detector.

Suitably, the VOC collector is configured to provide a specificconcentration by volume. Suitably, the VOC collector comprises a sorbentmaterial.

Suitably, the apparatus further comprises a pressure sensor configuredto measure atmospheric pressure.

Suitably, the apparatus further comprises a clock.

Suitably, the apparatus comprises a pump for pumping gas past the VOCconcentration analyser and the VOC collector in a downstream directionand the apparatus is configured whereby the VOC concentration analyserdetermines a VOC concentration at a predetermined time by the pumppumping borehole gas past the VOC concentration analyser and the VOCcollector for a pumping period. Suitably, the apparatus is configuredwhereby the pumping period, a time of measurement and an atmosphericpressure at the time of measurement are recorded.

Suitably, the apparatus comprises a pump for pumping gas past the VOCconcentration analyser and the VOC collector in a downstream directionand a filter for removing any of particulates or moisture from a gasinput, wherein the VOC concentration analyser and the VOC collector areupstream of the filter.

Suitably, the apparatus comprises a pump for pumping gas past the VOCconcentration analyser and the VOC collector in a downstream directionand there is a gas flow path comprising a gas input, a first valveupstream of the pump and a pressure sensor, wherein the apparatus isconfigured whereby with the first valve closed the pump is activated fora predetermined period and if within the predetermined period apredetermined pressure is not exceeded, as measured by the pressuresensor, a pump fail signal is generated. Suitably, the predeterminedperiod is between 8 and 12 seconds and the predetermined pressure is 100mb.

Suitably, the apparatus comprises a pump for pumping gas past the VOCconcentration analyser and the VOC collector in a downstream directionand there is a gas flow path comprising a gas input, a first valveupstream of the pump, a pressure sensor and a filter, wherein theapparatus is configured whereby with the first valve open a firstpressure sensor reading is taken, the pump is activated for apredetermined period after which a second pressure sensor reading istaken, and if the magnitude of the difference between the first pressuresensor reading and the second pressure sensor reading is greater than apredetermined value, a filter fail signal is generated. Suitably, thepredetermined period is between 2 seconds and 6 seconds. Suitably, thepredetermined value is 250 mb.

Suitably, the time of sensing and the length of time for which the pumpoperates are recorded

Suitably the apparatus comprises a second valve downstream of the firstvalve and a gas outlet.

Suitably, the apparatus is configured to have a borehole side and anatmospheric side, wherein there is a gas outlet to the borehole side ofthe device and to the atmospheric side of the device.

Suitably, the VOC concentration analyser and the VOC collector are inseries in a gas flow path with a gas analyser. Suitably, the gasanalyser analyses one or more of hydrocarbons, carbon dioxide, oxygenand hydrogen sulphide.

According to the present invention is a second aspect, there is provideda method of operation of an in-borehole gas monitor apparatus, whichmethod comprises the use of an in-borehole gas monitor apparatusaccording to the first aspect of the invention in a borehole.

Suitably, the VOCs collected by the VOC collector are quantified.

Suitably, the apparatus comprises a pump for pumping gas from theborehole past the VOC collector and the VOC analyser, wherein the timeof sensing and the length of time for which the pump operates arerecorded to determine the volume of gas passing through the apparatus.This enable the VOC concentration to be determined.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example only,with reference to the drawings that follow; in which:

FIG. 1 is a schematic illustration of a borehole site with anin-borehole gas monitor according to the present invention.

FIG. 2 is a schematic cross-sectional elevation of an in-borehole gasmonitor apparatus according to the present invention.

FIG. 3 is a schematic flow diagram illustrating a method of operation ofan in-borehole gas monitor apparatus according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1 of the accompanying drawings, there is shown aborehole 2 in ground consisting of a landfill site. The borehole 2 issupported by a liner 4 in which a plurality of side-holes 6 are locatedto allow for sampling.

Referring to FIG. 2 of the accompanying drawings, there is shown anin-borehole gas monitor (IGM) apparatus 8 including a cap 10. The cap 10comprises an inner bore 12 for receiving the IGM apparatus 8. The cap 10includes an exterior screw thread 14 for engaging with a correspondinginterior screw thread (not shown) on liner 4. Alternatively, the cap canbe made as part of the housing. A seal 16 is provided for fitting theIGM apparatus 8 in a borehole when a suitable screw thread is notavailable for the cap 10 to be used.

The IGM apparatus 8 consists of a body portion 17 which is aself-contained unit meeting environmental rating IP-68, i.e. essentiallywaterproof. The IGM apparatus 8 comprises a top 30 and an external tube32. The external diameter of tube 32 in this embodiment is approximately40 mm allowing for it to be inserted into a typical borehole liner. Inthis embodiment of the invention, the length of tube 32 is 800 mm, butmay be less.

The IGM apparatus 8 further comprises a gas inlet 36 connected to afirst entry valve 38, which gas inlet leads to a volatile organiccompounds (“VOC”) detector 40 connected to a VOC collector 42, connectedto a water and particulate filter 44 for removing any excess moistureand/or particles from the ingressed gases. The filter 44 is connected toa first pressure sensor 46, connected to a pump 48 connected to a gasdetector 50 comprising a plurality of gas analysers, in this case andH₂S and CO sensor 52, a CO₂ sensor 54, a CH₄ sensor 56 and an O₂ sensor58. The detector is connected to a second valve 60 which is connected toa return line (a first outlet) 62 back to the borehole and a branchedconnection to a third valve 64 which is connected to a second pressuresensor 66 from which extends a second outlet 68, this time toatmosphere.

A suitable filter 44 is an in-line particulate and moisture filter suchas that available from Geotechnical Instruments of Sovereign House,Queensway, Leamington Spa, United Kingdom.

The VOC detector 40 detects the presence and concentration of a range ofVOCs but does not distinguish between the various VOCs. A suitable VOCsampler 40 is a photo-ionisation detector. The VOC collector 42 is asorbent and sorbs (that is, adsorbs or absorbs) VOCs passingtherethrough. A suitable VOC sampler 40 would be a GORESorb (trade mark)tube with a multiplicity of small sorbent balls therein.

Any suitable gas variable can be measured in the detector 50, theanalysers typically being used to monitor hydrocarbons (especiallymethane), carbon dioxide, oxygen carbon monoxide and hydrogen sulphideconcentrations.

The IGM apparatus 8 further comprises a combined controller and memory70 for controlling operation of the apparatus 8 and a power cell(battery) 72 making the operation of the apparatus 8 self-contained,i.e. not reliant on data communication with or power from an externalsource. The controller 70 includes a clock.

A vent pipe 74 is provided running through the apparatus 8 from thebore-hole end to an outlet 76 through the top 30 to atmosphere (theatmospheric end of the apparatus). A vent pipe valve 78 is provided forthe vent pipe 64 to control whether it is open to atmosphere.

Also shown is a water detector 80, which detects the presence orproximity of liquid water in the apparatus and upon such detectiontransmits a signal to the controller 70. A conductance sensor is used todetermine a liquid water presence.

Further, a water level detector (not shown) can be connected to thebottom of the IGM apparatus and suspended therebelow in use into theborehole. As wired pressure transducer can be used.

The top 30 includes a connector 82 allowing data communication with aremote device and unit activation. Additionally, a pressure sensor canbe attached here for monitoring borehole water level.

The IGM apparatus 8 is mounted in a borehole 2, within a borehole linerwith the cap 10 providing a gas-tight seal.

Over time, gases will build up in the borehole 2. The IGM apparatus 8 isconfigured, specifically by programming of the controller 70, toautomatically and periodically test a gas sample from the borehole. Theprocess by which this is undertaken will now be described.

First (step 100) a pump test is carried out. With first valve 38 shut,the pump 48 is started and first pressure sensor 46 must read 100 mbwithin 10 seconds otherwise a FAIL warning is produced by controller 70as the pump 48 may have failed.

Next (step 102) a filter test is carried out. With first valve 38 openafter 4 seconds first pressure sensor 46 takes a pressure reading BH.The pump 48 then runs for a predetermined period and first pressuresensor 46 takes another pressure reading BHP. If BHP−BH>250 mb a FAILwarning is produced by controller 70 as the filter 44 is likely to havebecome blocked.

Any FAIL warnings appear prominently as part of a data download from theapparatus.

First and second valves 38 and 60 are opened (step 104) and pump 48 isactivated (step 106) to pump gas from the borehole through the gas flowpath described above to ensure the sensors have an up to date gas samplefrom the borehole. The VOC detector 40 and VOC collector 42 precede thefilter 44 which would otherwise remove the VOCs from the gas flow. VOC'scollected by the VOC collector can be quantified by removing the VOCcollector and eluting the VOC's into an instrument such as a gaschromatograph. Measurements (step 108) of VOC concentrations are made bythe VOC detector 40. Moisture and particulates are removed by the filter44.

Borehole gas then passes through the detector 50 where it is analysed by(step 110) by gas analysers 57, 54, 56 and 58.

A concurrent gas pressure measurement (step 112) is made by first gaspressure sensor 38 and a reference measurement of atmospheric pressureis made by second pressure sensor 66. The time of the sensing and lengthof time for which the pump is operated and recorded (step 114). Based onan empirical measurement or by calculation, the volume of gas passingthrough the apparatus 8 per unit time when the pump 48 is running can bedetermined. Accordingly, it can be determined what volume of gas haspassed through the apparatus in any given testing period. This data isstored in the controller/memory 70. The amount of VOC's collected by theVOC collector can then be divided by the volume of gas passed over thecollector giving a measure of VOC concentration.

First and second valves 38 and 60 are then closed (step 116). The gasfrom the borehole is circulated back to the borehole through theborehole end of the apparatus.

Gas variable measurements are carried out by the gas analysers 52, 54,56 and 58. Any appropriate variable can be monitored including one ormore of the presence or absence of a particular gas, a gas concentrationlevel, a gas pressure, moisture content in a gas, etc. The data from thegas variable measurements is stored in the controller/memory 70.

A timer in the controller 70 is re-set (step 116) so that a subsequentperiodic measurement can be made.

The data stored in controller/memory 70 can be downloaded over ahard-wired connection via the connector 82 or by wireless transmission.This connection can also be used to program the controller 70 to operatethe apparatus 8 as desired. For instance, variables such as thefrequency of sampling, whether sampling is regular or irregular, whetherthere should be a periodic venting to atmosphere, etc can be set.

On an ongoing basis if the water detector 80 detects the presence ofwater in the apparatus, a water detection signal is sent to thecontroller 70 which can take an appropriate step, such as deactivatingthe apparatus 8, transmitting an alert signal, illuminating a warninglight etc. This can both protect the apparatus 8 from damage and avoidcontaminated readings being made.

As gases build up in the borehole over time, it can be useful to openthe borehole to atmosphere to reduce the pressure therein, but also toprovide the opportunity to, in effect, re-start the sampling operationby allowing the borehole to equilibrate to atmosphere. Thus, the baseline for any monitoring can be re-set and an analysis of the variationof gas variables over time can be undertaken. The apparatus 8 can beconfigured to vent the borehole to atmosphere periodically or oninstruction.

Thus, there is provided a portable, self-contained IGM apparatus thatcan be conveniently deployed in a borehole to take periodic datareadings of gas variables in the borehole.

In particular, preferred embodiments of the present invention enableVOCs to be monitored. The combination of the VOC detector together withthe VOC collector and the determination of the volume of gas passingthrough the apparatus enables a calculation to be made of the absoluteconcentrations of specific VOCs in the borehole and also how they varyover time. By time-stamping the results, the variation of VOCs over timecan be monitored enabling, for instance, comparisons with othertime-variable phenomena, such as atmospheric pressure or weatherconditions.

Attention is directed to all papers and documents which are filedconcurrently with or previous to this specification in connection withthis application and which are open to public inspection with thisspecification, and the contents of all such papers and documents areincorporated herein by reference.

All of the features disclosed in this specification (including anyaccompanying claims, abstract and drawings), and/or all of the steps ofany method or process so disclosed, may be combined in any combination,except combinations where at least some of such features and/or stepsare mutually exclusive.

Each feature disclosed in this specification (including any accompanyingclaims, abstract and drawings) may be replaced by alternative featuresserving the same, equivalent or similar purpose, unless expressly statedotherwise. Thus, unless expressly stated otherwise, each featuredisclosed is one example only of a generic series of equivalent orsimilar features.

The invention is not restricted to the details of the foregoingembodiment(s). The invention extends to any novel one, or any novelcombination, of the features disclosed in this specification (includingany accompanying claims, abstract and drawings), or to any novel one, orany novel combination, of the steps of any method or process sodisclosed.

1. An in-borehole gas monitor (IGM) apparatus comprising a VOCconcentration analyser and a VOC collector.
 2. The in-borehole gasmonitor (IGM) apparatus of claim 1, wherein the VOC concentrationanalyser is configured to provide a non-specific real-time concentrationof VOCs.
 3. The in-borehole gas monitor (IGM) apparatus of claim 1,wherein the VOC concentration analyser comprises a photo-ionisationdetector.
 4. The in-borehole gas monitor (IGM) apparatus of claim 1,wherein the VOC collector is configured to provide a specificconcentration by volume.
 5. The in-borehole gas monitor (IGM) apparatusof claim 1, wherein the VOC collector comprises a sorbent material. 6.The in-borehole gas monitor (IGM) apparatus of claim 1, wherein theapparatus further comprises a pressure sensor configured to measureatmospheric pressure.
 7. The in-borehole gas monitor (IGM) apparatus ofclaim 1, wherein the apparatus further comprises a clock.
 8. Thein-borehole gas monitor (IGM) apparatus of claim 1, wherein theapparatus comprises a pump for pumping gas past the VOC concentrationanalyser and the VOC collector in a downstream direction and theapparatus is configured whereby the VOC concentration analyserdetermines a VOC concentration at a predetermined time by the pumppumping borehole gas past the VOC concentration analyser and the VOCcollector for a pumping period.
 9. The in-borehole gas monitor (IGM)apparatus of claim 8 wherein, the apparatus is configured whereby thepumping period, a time of measurement and an atmospheric pressure at thetime of measurement are recorded.
 10. The in-borehole gas monitor (IGM)apparatus of claim 1, wherein the apparatus comprises a pump for pumpinggas past the VOC concentration analyser and the VOC collector in adownstream direction and a filter for removing any of particulates ormoisture from a gas input, wherein the VOC concentration analyser andthe VOC collector are upstream of the filter.
 11. The in-borehole gasmonitor (IGM) apparatus of claim 1, wherein the apparatus comprises apump for pumping gas past the VOC concentration analyser and the VOCcollector in a downstream direction and there is a gas flow pathcomprising a gas input, a first valve upstream of the pump and apressure sensor, wherein the apparatus is configured whereby with thefirst valve closed the pump is activated for a predetermined period andif within the predetermined period a predetermined pressure is notexceeded, as measured by the pressure sensor, a pump fail signal isgenerated.
 12. The in-borehole gas monitor (IGM) apparatus of claim 11,wherein the predetermined period is between 8 and 12 seconds and thepredetermined pressure is 100 mb.
 13. The in-borehole gas monitor (IGM)apparatus of claim 1, wherein the apparatus comprises a pump for pumpinggas past the VOC concentration analyser and the VOC collector in adownstream direction and there is a gas flow path comprising a gasinput, a first valve upstream of the pump, a pressure sensor and afilter, wherein the apparatus is configured whereby with the first valveopen a first pressure sensor reading is taken, the pump is activated fora predetermined period after which a second pressure sensor reading istaken, and if the magnitude of the difference between the first pressuresensor reading and the second pressure sensor reading is greater than apredetermined value, a filter fail signal is generated.
 14. Thein-borehole gas monitor (IGM) apparatus of claim 13, wherein thepredetermined period is between 2 seconds and 6 seconds.
 15. Thein-borehole gas monitor (IGM) apparatus of claim 13, wherein thepredetermined value is 250 mb.
 16. The in-borehole gas monitor (IGM)apparatus of claim 8, wherein the time of sensing and the length of timefor which the pump operates are recorded.
 17. The in-borehole gasmonitor (IGM) apparatus of claim 11 wherein, the apparatus comprises asecond valve downstream of the first valve and a gas outlet.
 18. Thein-borehole gas monitor (IGM) apparatus of claim 1, wherein theapparatus is configured to have a borehole side and an atmospheric side,wherein there is a gas outlet to the borehole side of the device and tothe atmospheric side of the device.
 19. The in-borehole gas monitor(IGM) apparatus of claim 1, wherein the VOC concentration analyser andthe VOC collector are in series in a gas flow path with a gas analyser.20. The in-borehole gas monitor (IGM) apparatus of claim 19, wherein thegas analyser analyses one or more of hydrocarbons, carbon dioxide,oxygen and hydrogen sulphide.
 21. A method of operation of anin-borehole gas monitor apparatus, which method comprises the use of anin-borehole gas monitor apparatus according to claim
 1. 22. The methodof operation of an in-borehole gas monitor apparatus of claim 21,wherein the VOCs collected by the VOC collector are quantified.
 23. Themethod of operation of an in-borehole gas monitor apparatus of claim 21,wherein the apparatus comprises a pump for pumping gas from the boreholepast the VOC collector and the VOC analyser, wherein the time of sensingand the length of time for which the pump operates are recorded todetermine the volume of gas passing through the apparatus. This enablesthe VOC concentration to be determined.